1. Field of the Invention
The present invention relates to a method to store data on writeable optical disks, and more particularly to the use of marks in the wobble of the groove to store data.
2. Description of Related Art
FIG. 1 illustrates a writable optical disk that has tracks formed from a single spiral groove. The writable optical disk is, for example, a record-able CD or DVD. The spiral groove increases in diameter linearly with increasing radius in a mathematical phenomenon known as the Archimedes Spiral. The interval between turns of the spiral groove is called the track pitch and this is nominally constant for most optical disks. The groove is divided into tracks that each form a 360-degree turn of the groove. The tracks are further divided into sectors, which are the smallest units that an optical drive (including reader and writer) accesses. The optical drive keeps track of where data is stored by the data's sector number.
To determine the linear velocity of the tracks, the tracks in the writable area contain a deviation from the averaged centerline of the groove called “wobble.” FIG. 2 illustrates the wobble. Optical drives measure the number of cycles during a unit of time (frequency) to determine the linear velocity of the track. Optical drives match the clocks used to write data into the tracks (“write speed”) with the linear velocity of the tracks so that the written bits of data are equally spaced apart. For further details, see for example U.S. Pat. No. 4,972,401 issued to Carasso et al.
Writable optical disks must have a reliable method for reading radial and rotational positions of the tracks so that optical drives can read from and write to the appropriate locations in the tracks. Radial and rotational information may be communicated through prewritten data in the tracks called pre-embossed headers. In this addressing scheme, the mastering equipment creates the optical disks with radial and rotational information written in the groove during the manufacturing of the optical disks. This addressing scheme displaces some storage area that can be otherwise used to store user data in order to store radial and rotational information. For further details, see for example Standard ECMA-272 from ECMA located at 114 Rue du Rhône —CH-1204 Geneva Switzerland (“ECMA”), which is hereby incorporated by reference.
Radial and rotational information may also be communicated by modulating the frequency of the wobble. The wobble frequency is modulated between a first frequency and a second frequency to communicate an active or inactive bit (e.g., a “1” or a “0” bit). This addressing scheme is inefficient because multiple wobble cycles are required to convey an active or inactive bit. As FIG. 2 illustrates, the wobble may include periodic occurrences of square waves called “Alternating Fine Clock Marks” (“AFCMs”) that provides timing information. Each AFCM has an amplitude 3.5 to 7 times greater than the amplitude of the wobble. Each AFCM is inverted from the AFCM in the adjacent tracks. The AFCMs are spaced equally apart around the tracks to provide timing information. For further details, see for example Standard ECMA-274 from ECMA, which is hereby incorporated by reference.
Radial and rotational information may further be communicated through a series of pits (“land pre-pits”) on the land areas between the tracks. Land pre-pits create cross talk into the data because optical drives detect the land pre-pits in the land areas between the tracks. Closely aligned land pre-pits in adjacent tracks also create cancellation problems as their presence cancels their detection by optical drives. Land pre-pits further require a 2-beam mastering system that can generate the groove and the land pre-pits simultaneously during the mastering of the optical disks. For further details, see for example Standard ECMA-279 from ECMA, which is hereby incorporated by reference.
A master optical disk is formed by coating a glass substrate with a photoresist, exposing the photoresist to a laser beam recorder, developing the photoresist, removing the photoresist, and coating the remaining material with a thin seed-layer of metal to form the master optical disk. These steps are known as “mastering”. A stamper is made by electroplating nickel onto the master and removing the nickel from the master to form the stamper. These steps are known as “electroforming”. Optical disks are produced from the stamper by placing the stamper in a mold cavity of an injection molding press and injecting molten plastic into the mold. The resulting molded disks have an imprint of the stamper. These steps are known as “molding”. The molded disks are then coated with a variety of thin films (e.g., reflective layers, active layers, overcoats) depending on their type. The molded disks can be coated by a variety of methods, such as sputtering, spin coating, and chemical vapor deposition (CVD). Manufacturers of optical disks include Ritek of Taiwan, Sony of Japan, Matsushita of Japan, and Imation of Oakdale, Minn.